Superhigh-pressure mercury vapor discharge lamps



y 1968 T. HOLMES ETAL 3,382,396

SUPERHIGH-PRESSURE MERCURY VAPOR DISCHARGE LAMPS Original Filed March 50, 1964 INVENTOR. THOMAS HOLMES ABRAHAM TIMM ER MANS United States Patent 3,382,396 SUPERHIGH-PRESSURE MERCURY VAPOR DISCHARGE LAMPS Thomas Holmes and Abraham Timmermans, Emmasingel, Eindhoven, Netherlands, assignors to North American Philips Company, Inc., New York, N.Y., a corporation of Delaware Continuation of application Ser. No. 355,667, Mar. 30, 1964. This application Mar. 13, 1967, Ser. No. 622,828 Claims priority, application Netherlands, Apr. 3, 1963,

291,092 4 Claims. (Cl. 313-228) The present application is a continuation of application Ser. No. 355,667, filed Mar. 30, 1964, now abandoned.

The invention relates to a superhigh-pressure mercury vapor discharge lamp, that is to say a lamp in which during operation with the prescribed load a pressure prevails which exceeds 15 atmospheres.

Superhigh-pressure mercury vapor discharge lamps nearly always comprise solid electrodes of a high-meltingpoint conductor material, mostly tungsten, these electrodes being spaced apart by a distance exceeding twice the smallest inner diameter of the discharge space. Apart from mercury vapor, the discharge space of these lamps contains a small quantity of ignition gas, preferably a rare gas or a mixture of rare gases. The wall of such discharge lamps is always subjected to very heavy thermal load, generally in excess of 300 w./cm. of the inner surface, as a result of which the temperature thereof becomes very high during operation. In order to allow this high load on the wall, two steps have been taken.

Firstly, the wall of the discharge space is cooled, for example by means of a flow of water and, secondly, quartz glass is used as material for the wall. With the use of these steps, the temperature of the inner side of the wall of the discharge space may exceed 600 C. without the occurrence of a mechanical deformation of the wall after the lamp has burned for a few hours.

The life of such lamps is generally limited by the instant at which the lamp becomes leakly as a result of cracks in the wall of quartz glass. These cracks are probably due to variations in structure, possibly crystallization of the quartz glass.

A superhigh-pressure mercury vapor discharge lamp in accordance with the invention comprising solid electrodes of a high-melting-point conductor material which are spaced apart by a distance exceeding twice the smallest inner diameter of the discharge space, and a quartz glass wall surrounding the discharge space which is often becomes leaky due to cracks in the quartz glass envelope. If, according to the invention, a slight quantity of halogen is introduced into the discharge space, either the life time of the lamp is considerably lengthened with the same load, or the load can be increased with the same life time.

Since the introduction and dosage of halogen as such into these very small discharge lamps is very difficult, the halogen is preferably introduced into the discharge space while being bound to an alkali metal. Consequently, the discharge space contains per g.-atom of halogen 1 g.- atom of alkali metal. However, the quantity of halide is always so small that no lines from the elements bound to the halogen are observable in the spectrum of the emitted light.

Particularly satisfactory results are obtained with sodium iodide and sodium bromide, since they are comparatively nonhygroscopic and since they substantially do not raise the ignition voltage of the lamps.

The invention will now be described more fully with reference to a few embodiments and to a drawing showing a superhigh-pressure mercury vapor discharge lamp in accordance with the invention.

In the drawing, reference numeral 1 denotes the quartz glass bulb enveloping the discharge space 2. This discharge space 2 comprises a cathode 3 and an anode 4 which both consist of tungsten. The electrodes 3 and 4 are connected through fusing strips 5 and 6 of molybdemum to current supply conductors 7 and 8. The discharge space 2 contains mercury, a rare gas and a halogen, for example iodine.

A great number of lamps were manufactured in accordance with this drawing, different quantities of iodine being introduced in the discharge space 2. The discharge space of all lamps contained, apart from the iodine, 6.5 x 10- gms. of mercury and such a quantity of argon that the pressure thereof was 60 mm. of mercury column at room temperature. In all test lamps, the volume of the discharge space was approximately 1(lcm. The lamps were fed with a pulsatory direct current of a mean value of 2 A at a mean voltage of 400' v. and a pulse frequency of 72 pulses per second. The iodine was introduced into the discharge space while being bound to sodium.

The table below indicates the mean life of the test lamps as a function of the quantity of iodine in g.-atoms per cm. Also the number of test lamps is indicated with which the mean lifetime is determined for each quantity of iodine.

Number of measured lamp Mean lifetime in hours loaded during operation with more than 300 w. per cm? of the inner surface, is characterized in that the discharge space contains per cm. from 5X10 to 5 X10 g.-atom of at least one of the halogens.

It is known to introduce into mercury vapor discharge lamps, having liquid mercury electrodes and a glass wall, halides of metals, particularly of the alkali metals, in such a quantity that the emitted light not only exhibits the lines of the mercury spectrum, but also the lines of the spectrum of the metal bound to the halogen, for example alkali metal. It is said of these known lamps that the glass wall is not attacked in contrast with lamps which contain the said metals, for example alkali metals, but which do not contain halogen.

It was found that with super-high-pressure mercury vapor discharge lamps, as already stated above, the lamp As already stated above, the iodine is introduced into the discharge space in the form of sodium iodide. In the spectrum emitted by the lamp, however, no lines of the sodium could be observed.

The introduction of sodium chloride or sodium bromide into the discharge space instead of sodium iodide resulted in an analogous lengthening of life.

What is claimed is:

1. A superhigh-pressure mercury vapor lamp comprising an envelope having a quartz glass wall portion surrounding a discharge space, electrodes within said onvelope for producing a discharge in said space spaced apart a distance exceeding twice the smallest inner diameter of the discharge space, a supply of mercury within said discharge space and an inert gas at a pressure at which a discharge is produced between said electrodes which produces a load of at least 300 w./crn. on the inner surface of said wall portion, and between 5 10 and 5 l0- grarn-atoms/cm. of azhalogen in saiddischarge space whereby the life of said lamp is greater than the same lamp without the halogen and no spectral lines of an element bound to the halogen are emitted.

2. A superhigh-pressure mercury vapor lamp as claimed in claim 1 in which the halogen is present in the form of an alkali halide.

3. A superhigh-pressure mercury vapor discharge lamp as claimed in claim 2 in which the alkali metalis sodium and the halogenis selected from the group consisting of bromine and iodine.

UNITED STATES PATENTS 7 3,259,777 7/1966 Fridrich 313-229 JAMES W. LAWRENCE, Primary Examiner.

10 STANLEY D. SCI-ILOSSER, Examiner.

R. JUDD, Assistant Examiner. 

1. A SUPERHIGH-PRESSURE MERCURY VAPOR LAMP COMPRISING AN ENVELOPE HAVING A QUARTZ GLASS WALL PORTION SURROUNDING A DISCHARGE SPACE, ELECTRODES WITHIN SAID ENVELOPE FOR PRODUCING A DISCHARGE IN SAID SPACE SPACED APART A DISTANCE EXCEEDING TWICE THE SMALLEST INNER DIAMETER OF THE DISCHARGE SPACE, A SUPPLY OF MERCURY WITHIN SAID DISCHARGE SPACE AND AN INERT GAS AT A PRESSURE AT WHICH A DISCHARGE IS PRODUCED BETWEEN SAID ELECTRODES WHICH PRODUCES A LOAD OF AT LEAST 300 W./CM.2 ON THE INNER SURFACE OF SAID WALL PORTION, AND BETWEEN 5X10-5 AND 5X10-7 GRAM-ATOMS/CM.3 OF A HALOGEN IN SAID DISCHARGE SPACE WHEREBY THE LIFE OF SAID LAMP IS GREATER THAN THE SAME LAMP WITHOUT THE HALOGEN AND NO SPECTRAL LINES OF AN ELEMENT BOUND TO THE HALOGEN ARE EMITTED. 